1. Field of the Invention
This invention relates to an apparatus for electrically detecting a focal point of cameras or the like optical devices such as a microscope, high density optical recording and reproducing device or the like with the aid of a picture image signal treating circuit or the like.
2. Description of the Prior Art
As a conventional apparatus for electrically detecting a focal point of cameras or the like optical devices, it has been proposed to use a light receiving device including a number of light detecting elements, project an optical image whose focal point is to be detected on the light receiving device so as to obtain a picture element information from each of the light detecting elements, and obtain a focal point detecting signal on the basis of such picture element information. In this case, a number of picture element informations are obtained. In order to treat these picture element informations so as to obtain the focal point detecting signal, it is necessary to carry out complex steps. In general, it is preferable to digitally treat the picture element informations. In this case, it is a matter of course that an illumination intensity information obtained from each picture detecting element must be converted into a digital information. Various kinds of apparatuses for treating the illumination intensity information from a number of picture element informations for the purpose of detecting the focal point of the cameras or the like optical devices have heretofore been proposed. In all of these conventional apparatuses, each picture element is scanned by a light image in succession to derive corresponding illumination intensity as an analog amount which is then converted in succession into a digital amount. As a result, if the number of the picture elements becomes large, a considerably long time is required for the analog-digital conversion. In order to eliminate such drawback, if use is made of analog-digital converters which are the same in number as the picture elements for the purpose of simultaneously effecting all of the analog-digital conversions in parallel, a significantly large number of the analog-digital converters are required, thereby making the apparatus complex in construction.